1. Field of the Invention
This invention relates to thin film magnetic head fabrication procedures in general and, more specifically, to a method that utilizes sputtered and plated high magnetic moment material in combination with a pole stitching process.
2. Description of the Related Art
Thin film magnetic read/write heads are used to decode and encode magnetically stored information on moving magnetic media such as tapes and discs. Typically, the reading portion of the head, as presently constructed, is a small sensor, utilizing giant magneto-resistive structures (GMR), that converts rapid magnetic field fluctuations into resistance variations and thence into voltage variations. The write portion of the head consists of two pole pieces separated by a narrow gap and yoked together to form an approximately horseshoe-shaped assembly. A conductive coil is patterned between the pole pieces which, when electrically energized, induces a magnetic field between the poles which fringes across the gap. It is this induced field that encodes small magnetic regions in the moving medium.
The rapid changes in the state of the art have necessitated continual improvements in the area density of information that can be magnetically encoded and decoded in the moving medium. For a disk, this area density is a product of the number of recording tracks per mm measured radially, and the number of flux reversals per mm along the track, measured tangentially. With the development of the extremely sensitive magneto-resistive read heads, methods for improving the area density are now focussing on extending the limits of the inductive writing technology.
There are several approaches to improving the writing technology, each of which has shortcomings to be overcome. Clearly, one way to improve area density is to narrow track widths and thereby increase the number of tracks per mm. This approach requires that the writing tip of the magnetic pole assembly be made as narrow as possible and/or that the lateral fringe fields extending from the pole face be eliminated or reduced. Ohtsuka et al (U.S. Pat. No. 5,774,308) teach a method for designing a thin film inductive head that suppresses the spread of the writing magnetic field at the air bearing surface (ABS) of the pole face. While the lateral width of the pole face determines the effective track density, the vertical width of the write gap determines the linear density along the track. Chen et al (U.S. Pat. No. 5,282,308) find that small pole faces and narrow gaps can be more efficiently fabricated if the upper pole piece and yoke assembly are formed as separate parts and then "stitched" together at a pedestal structure. This stitching mechanism will play a role in the invention set forth herein. Chang et al (U.S. Pat. No. 5,805,391) teach a method of forming a stitched pole wherein the pole tip is placed close to the flared yoke so as to optimize the magnetic field from the ABS portion of the pole tip. Santoni (U.S. Pat. No. 5,901,431) teaches a method for forming a narrow pole piece and narrow gap without stitching, but by using a single photolithographic and plating process.
There are other problems associated with the necessity of inducing strong, rapidly varying magnetic fields in the pole structure. One problem has to do with the creation of undesireable eddy currents within the pole pieces. Another problem is the requirement of using magnetic materials that can both sustain high magnetic fields and have them change rapidly. The eddy current problem can be resolved by using magnetic materials with high resistivity. The magnetic moment problem can be resolved by using magnetic materials with high magnetic moments and low coercivity. A wider range of such materials becomes available if they can be deposited by sputtering rather than the more commonly used method of electroplating. Sato et al (U. S. Pat. No. 5,894,388) teach a method of forming magnetic pole structures out of such soft magnetic materials by sputtering them on a core of non-magnetic material. Van der Zaag et al (U.S. Pat. No. 5,904,996) teach a method of manufacturing a magnetic field sensor by a Ne--He sputtering technique. However, electroplating techniques are not completely ruled out, according to a method taught by Calhoun et al (U.S. Pat. No. 5,883,762). Sputtered films have as a shortcoming, the fact that they often contain residual internal stresses. Kira et al (U.S. Pat. No. 5,225,951) teach a sputtered yoke process that incorporates a method for compensating internal stresses and, thereby, preventing the degradation of magnetic properties.
The present invention differs from all those cited above in that it combines the fabrication advantages of the stitched pole process with the material advantages of high magnetic moment magnetic materials.